1. Field of the Invention
The invention relates to a spark plug, comprising a longitudinal bore formed in a housing for receiving an insulator, with the housing having a first bore for receiving a pressure measuring device.
2. The Prior Art
A spark plug with a continuous longitudinal bore arranged off-center in the housing for receiving an insulator is known from AT 407.577 B. The spark plug comprises housing regions of different wall thicknesses, with a pressure measuring device being arranged in a region of larger wall thickness. The bore for receiving the pressure measuring device is arranged in an inclined manner with respect to the longitudinal bore.
A spark plug for internal combustion engines is known from AT 002.228 U1 which comprises an optical sensor integrated in the spark plug with several light guides opening into the combustion chamber. The light guides are arranged concentrically around the axis of the middle electrode. A group each of bores extending parallel to the axis of the spark plug open into a collecting bore arranged as a pocket hole. The optical connection is made via light guide cables and the light guides opening into the combustion chamber via the collecting bore and the bores.
AT 003.845 U1 describes an optoelectronic measuring device for detecting combustion processes in the combustion chamber of an internal combustion engine in operation, with the optical sensors being arranged in a component which is essentially cylindrical and opens into the combustion chamber and the sensor ends are substantially arranged radially on the jacket of the component. The component can be arranged as a spark plug for example.
A spark plug with a force-measuring element for measuring the pressure applied to the spark plug is further known from AT 402.116 B, with the insulating body of the spark plug resting on the spark plug housing by interposing the force-measuring element when pressure is applied in the axial direction.
Known spark plugs are thus combined either with a pressure sensor or an optical sensor. It was not known or even regarded as feasible to house and produce both an optical sensor as well as a pressure sensor in a spark plug.
A parallel optical measurement and pressure measurement is inevitable in order to enable the monitoring of combustion processes in real time. As a result of the compact arrangement of the charge-changing valves, the injection devices and the spark plugs, it is increasingly difficult to arrange additional bores in the cylinder head for the optical monitoring of the combustion chamber and/or the pressure monitoring of the combustion chamber. That is why it is desirable to keep the number of measuring bores as low as possible. One possibility of avoiding these additional bores is to adapt an additional measuring function in the spark plug.
It would be desirable to perform pressure measurement and light measurement at the same point in order to offer a high amount of significance in the evaluation of combustion processes.
It is the object of the invention to further develop a spark plug of the kind mentioned above in such a way that connection dimensions of a conventional spark plug are achieved and optical measurements and piezoelectric pressure measurements can be performed in parallel.